About Half of Earths Internal Heat Comes From Radioactive Decay

About half of Earths internal heat comes from radioactive decay, while much of the rest is ancient heat left over from the planets formation.

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Earth is still carrying enormous heat from its formation roughly 4.5 billion years ago, while radioactive elements inside rocks continue adding heat today. The two sources are often described as primordial heat and radiogenic heat. Radioactive decay, mainly involving uranium, thorium, and potassium, releases energy slowly throughout Earths crust and mantle. Estimates commonly put radiogenic heat at about half of Earths present internal heat budget, although the exact split remains uncertain. The rest is largely leftover energy from the planets formation and early differentiation. Earths total internal heat flow to the surface is estimated at roughly 43 to 49 terawatts. That heat does not simply sit inside a molten planet. It moves through a layered, mostly solid Earth, with slow mantle convection playing a major role in transporting deep heat. This internal energy helps drive mantle motion and plate tectonics, while heat leaving the core also supports the processes that maintain Earths magnetic field. The distinction matters because surface warmth is dominated by sunlight, whereas geothermal heat comes from inside the planet. The radioactive contribution is also important to Earth science because radioactive decay provides both an ongoing heat source and a basis for radiometric dating. Together, these processes explain why Earth has remained geologically active for billions of years instead of simply cooling into a completely inactive world.

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